An online calculator has been taken down from Inland Revenue's (IRD) website after it was revealed it could cause people to overpay their taxes.
IRD says it's urgently working to fix the issue with its Fair Dividend Rate calculator, which was producing incorrect results.
The Fair Dividend Rate is a method used to work out how much a foreign investment portfolio should be taxed.
According to Stuff, the online tool was calculating the gross profit of investors as opposed to net profit, while "quick sale" losses also weren't being subtracted.
IRD confirmed to Newshub the calculator had been removed from its website.
"We apologise to any customers affected by this," a spokesperson said.
Individual tax returns are due on Wednesday, meaning many would have already filed.